I'm no guru, but what probably happened is that it didn't really "stay the same:" A 29 is only slightly lower than your current average (30.235 x2), so your average probably dropped by less than 0.01 but you don't see it because the average (as shown) only has 2 decimal places.
For example, your average may have been 60.474; now it is 60.471 ... but in both cases it is shown as 60.47.